There is known a catheter which is used for diagnosing the inside of a body lumen by ultrasonic waves by inserting the catheter into the body lumen such as a blood vessel. An example of such a catheter is disclosed in Japanese Patent No. 3954888.
The catheter described in Japanese Patent No. 3954888 includes a catheter main body having a lumen, and a shaft which is inserted into the lumen of the catheter main body and has a ultrasonic oscillation unit which emits ultrasonic waves at the distal end portion. The catheter allows the shaft which is inserted into the lumen of the catheter main body, to rotate around the axis thereof, as well as move in the proximal end direction, and so it is possible to obtain an ultrasonic image of a blood vessel wall. In addition, when the ultrasonic image is obtained, the operation thereof is performed by filling the lumen, that is, in a gap which is formed between the inner circumferential surface of the catheter main body and the outer circumferential surface of the shaft with a liquid, for example, such as physiological salt solution. This gap is to some extent secured larger, to the extent that when filling with a liquid, the filling can be easily and quickly performed.
In a case where the catheter main body is configured by a resin, as a member of the proximal end side of the catheter main body, a tube in which the outer diameter is relatively large in order to secure sufficient rigidity is used. On the other hand, as a member of the distal end side of the catheter main body, a tube in which the outer diameter is relatively small is used, to facilitate inserting into the body lumen, or the like. Then, these tubes are jointed to form the catheter main body. Therefore, the outer diameter of the distal end portion of the tube of the proximal end side needs to be smaller in accordance with the size of the tube of the distal end side.
In addition, the inner diameter of each tube needs to be set to the predetermined value or more so that the resistance does not become big when filling a liquid into the gap between the inner circumferential surface of the catheter main body and the outer circumferential surface of the shaft.
In addition, with the above-described proximal end side tube having the relatively large outer diameter at the proximal end side and being configured such that the outer diameter of the distal end portion is relatively small, the reachability to the deep blood vessel and the flexibility are enhanced, and there is a need to improve priming performance by setting the inner diameter to the predetermined value or more.
Examples of methods of manufacturing a medical tube like the above-described proximal end side tube include grinding, thermoforming, and the like with respect to a tube for processing having a certain outer diameter and a certain inner diameter.
However, in a method involving grinding the outer circumferential surface of the tube for processing, since the outer diameter of the tube for processing does not become the inner diameter or less and the thickness becomes too thin, there is a risk of breaking the tube when using.
In addition, in a method of decreasing the outer diameter and the inner diameter at the same time, by performing thermoforming, with respect the tube for processing, it is difficult to make the outer diameter small while securing the inner diameter to the predetermined value or more.